It is advantageous in many ophthalmic surgical procedures for the pupil to be dilated as much as possible. A pupil is dilated when the iris retracts towards the outer edges of the eye. This normally occurs when the eye is deprived of bright light, for example, at night.
When performing ophthalmic operations, such as replacing the lens of a patient's eye with an artificial intraocular lens, a dilated iris and pupil gives the surgeon a larger area to manipulate surgical instruments in order to operate on the human lens. The more area available to the surgeon reduces the risk of damaging the iris or other components of the eye due to unintentional contact with the surgical instruments.
A common method of dilating the pupil is the use of chemical eyedrops. The eyedrops are formulated to trigger the expansion of the iris, resulting in a dilated pupil. However, such eyedrops are not effective on all patients and more surgically complicated measures are often required. Also, such eyedrops can "wear off" during an operation resulting in the iris retracting and reducing the pupil size.
One method to dilate and maintain a pupil in the dilated state involves making four minor incisions at roughly 90.degree. intervals around the periphery of the cornea and inserting a small hook-like apparatus through each incision. The hooks engage with the inner circumferential edge of the iris and when retracted, pull the iris outwards to define an enlarged substantially square shaped opening. Another method, known as a sphincterotomy, involves making an incision into the cornea through which a blade is passed that makes radial cuts into the iris itself, thus allowing the iris to dilate and expose more of the lens. Both the above methods add extra time to the actual operation being performed and the latter involves considerable risk or damage to the patients iris. Moreover, the damage done in segmenting the iris during a sphincterotomy is irreversible and results in a permanently disfigured iris.
It is an object of the invention, to overcome or ameliorate at least some of the deficiencies of the prior art.